Control network



June 17, 1941. N. P. CASE CONTROL NETWORK Original Filed Feb. 11, 1938 in? Y n1 oz NdE INVENTOR yLSON P. CASE ATTORNEY Reissue'd June 17, 1941 coN'rnor. NETWORK Nelson P. Case, Great Neck, N. Y., assignor to Haaeltine Corporation, a corporation or Delaware Original No. 2,197,516, dated April 16, 1940, Serial No. 189,992, February 11, 1938. Application for reissue May 16, 1940, Serial No. 335,617

8 Claims. -(Cl. 250-20) This invention relates generally to a control network for modulated-carrier signal receivers and particularly to a silencing network to be utilized in a receiver including a tuning indicator such as the cathode-ray tuning eye. Also, the

invention is particularly suitable ioruse in a receiver in which a plurality of vacuum tubes in the signal-translating channel of the receiver have their cathodes directly grounded.

-It is desirable to incorporate in certain radio receivers both a visual tuning indicator and an arrangement for silencing the receiver during the intervals when the receiver is mistuned, to prevent distorted signals and noise from being reproduced. Many such silencing networks are known, the use of which is attended lay certain disadvantages. One of the disadvantages of the prior art silencing networks is that they have generally utilized at least one additional vacuum tube or its equivalent.

There is no potential available in the conventional radio receiver suitable to be utilized as a silencing voltage for the receiver without :Iur-

ther amplification. Furthermore, the silencing means previously utilized have generally been,

more responsive .to strong signals than to weak ones, the receiver being silenced for a lesser degree of mistuning when weak signals are being received. r a

One silencing network which has been used commercially. comprises a first audio-frequency lamplifienhaving a normal cathode potentlal'several volts above ground and a silencing network coupled to the signal channel of the receiver at a point preceding the first audio-frequency amplifier. rect current amplifier having a grounded cathode. for amplifying the automatic amplification'i control voltage of the receiver to provideja silencing voltage for' the first audio-irequency amplifier tube. The silencing voltage thus provided is applied positively to the control grid of the first audio-frequency amplifier, but is of such value that the bias 0! the control grid is not raised above its normal cutoff value except when the receiver is properly tuned. Howits cathode which,,as:stated above, is several This silencing network comprises a di-' the receiver is precisely tuned.

below ground potential.

volts above ground. As there is a relatively high amplification in the signal-translating channel of the receiver succeeding the point at which these alternating potentials are introduced, difllculty is experienced in preventing a low-frequency hum in the loud-speaker oi the receiver. If the same type of silencing network is utilized in a receiver having the cathode of the first audiofrequency amplifier grounded, it follows that the cathode of the amplifier which amplifies the automatic volume control potential is several volts Thus, in the conventional receiver circuit, the automatic amplification control source must provide potentials more ing channel of the receiver preceding the point from which the automatic amplification control potential is derived must also be more negatively biased, a condition which is obviously undesirable.

It is an object of the invention to provide an improved and economical control network for modulated-carrier signal receivers. 4

It is an object of the invention to provide a simple and economical silencing arrangement for a modulated-carrier signal receiver comprising a cathode-ray tuning indicator.

It is a further object oi the invention to provide a signal receiver including a silencing network having a substantially uniform response to received signals of varying intensity.

It is another object-of the invention to provide a sharply selective silencing network for a signal receiver to ensure silencing except when In accordance with the present invention, there is provided a modulated-carrier signal receiver, which may .be of the superheterodyne type, includingan automatic amplification control system for maintaining the signal amplitude at a given point in the receiver, for example, at a point in the intermediate-frequency channel, within relatively narrow limits. iter-amplifier is coupled to this point for deriving a signal substantially free from residual variations in amplitude, the limiter-amplifier including .a sharply-selective circuit tuned to the signal-carrier frequency and following the point at which limiting occurs. There is also provided means including a rectifier coupled to the limiter-amplifier for deriving a potential to silence the receiver. In a preferred embodiment of theinvention, the receiver includes a cathode- A lima carrier-frequency signal, an amplitude-limiter for limiting to a substantially constant value the maximum amplitude of signals translated thereby. a rectifier, and a circuit sharply-selective to the carrier-frequency signal and coupling the limiter to the rectifier. The control network also comprises means for applying the carrier-frequency signal to the limiter and rectifier, means for deriving directly from the rectifier a unidirectional control voltage for the receiver which is substantially free from residual variations in amplitude, and means for utilizing the control voltage to control an operating characteristic of the receiver.

As used herein, the term limiter-amplifier refers to an amplifier which is operated beyond both an upper and a lower cutoff point, so that signal inputs of all amplitudes in excess of a predetermined valuetransmitted by the amplifier develop output signals of constant amplitude; for example, the term may refer to a vacuum-tube amplifier adapted to operate over its entire grid-voltage plate current characteristic curve between negative grid-bias cutoif and the grid current point.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Figs. 1 and 2 are circuit diagrams, partly schematic, 'of complete super-'- heterodyne receivers embodying different forms of the invention. 1

Referring now more particularly to Fig. 1 of the drawing. there is shown schematically a complete superheterodyne radio receiver of a conventional design embodying the present invention in a preferred form. In general, the receiver includes a radio-frequency amplifier Ill having its input-circuit connected to an antenna l I and ground I! and its output circuit connected to an oscillator-modulator or frequency changer l3. Connected in cascade with frequency changer l3, in the order named, are an intermediatefrequency amplifier H of one or more stages and a duplex diode-triode vacuum tube I5, the diode section of which 'is the detector of the receiver and the triode section of which is the first audiofrequency amplifier of the receiver. The detector section of tube I5 is coupled to the output circuit of intermediate-frequency amplifier l4 through a double-tuned intermediate-frequency selector l8l9202l. A load circuit is provided for the detector comprising resistors 22 and 23 by-passed for carrier-frequency currents by condensers 24 and 21. Cathode-biasing resistors 25 and 26 are provided for vacuum tube I5. Audio-frequency potentials are derived from an adjustable voltage divider across resistor 23, com-- prising blocking condenser 26, adjustable tapped resistor 23, resistor 30, and by-pass condenser 48, by way of a volume control tap 3! on resistor29, and are applied to the grid of the triode section of the tube I5 in a conventional manner.

It will be understood that the various circuits just described may be of conventional construction and operation, the details of which are well known in the art, rendering further description thereof unnecessary. Considering briefly the operation of the receiver as a whole and neglecting for the moment the silencing network of this invention presently to be described, a desired received signal intercepted by antenna II is selected and .amplified by radio-frequency amplifier II), is converted to a modulated intermediatefrequency carrier in frequency changer i3, is amplified and selected by intermediate-frequency amplifier I4, and rectified by the diode section of tube 15, thereby, deriving the audio frequencies of modulation and the automatic amplification control bias. The audio-frequencies of modulation are, in turn, amplified by the triode section of tube l5 and by audio-frequency amplifier l6 and are reproduced by sound reproducer l1.

Referring now more particularly to the parts of the system involving the present invention, there is provided a means for developing an automatic amplification control bias for the receiver, for operatively exciting a cathode-ray tuning indicator or tuning eye 36, and for developing a voltage for silencing the receiver during tuning thereof or when mistuned. A voltage derived from the intermediate-frequency channel of the receiver is amplified to a. constant value by limiter-amplifier 31 having its control grid coupled to the output circuit of intermediatefrequency amplifier l4 through condenser 38. An automatic amplification control bias derived from grid leak 38' is applied to the control electrodes of one or more of the tubes of radio-frequency amplifier Ill, oscillator-modulator i3, and intermediate-frequency amplifier l4 to maintain the signal input to the detector within a relatively narrow range for a wide range of received signals. ,,A cathode-biasing resistor 39, by-passed by condenser 40, is provided for limiter-amplifier 31. The output circuit of limiter-amplifier 31 is coupled through a sharply tuned loosely-coupled transformer 4|, 42 to a diode section in limiteramplifier 31 provided with a load circuit comprising resistor 43 by-passed by condenser 44, across which a unidirectional voltage is developed. The unidirectional voltage across resistor 43 is applied to the input electrode of a cathode ray tuning eye tube 36 through a filter comprising a series resistor. 45 and a shunt condenser 46, the anode of tube 36 being connected directly to the common terminal of resistors 23 and 36 in the audio-frequency load circuit of detector l5. Auxiliary anode 41 is the targetof tuning eye tube 36. Suitable operating potentials are provided'in a conventional manner for the various tubes of the receiver through the terminals indicated as +Sc and +3.

In considering the operation of the arrangement just described, it will first be assumed that no signals of an appreciable amplitude are being received. Under these conditions the control grid of tuning-indicator tube 36 is substantially at ground potential, the resistance of the output circuit of the tuning-indicator tube is low, and a wide angle shadow is developed on the target of indicator tube 36 to show that the receiver is not tuned to a sending station. Under the conditions assumed, the conductance of tube 36 is high resulting in an appreciable voltage drop across resistor 30. It will be seen that this voltage across resistor 30 is eifectively a bias upon the control grid of the triode section of the duplex tube l5 and that, under the conditions assumed,

the triode section is efiectively cut oil and the receiver is silent. When the receiver is tuned to a signal at any usable strength, the intermediatefrequency carrier at the receiver is amplified by limiter-amplifier "31 and rectified in thediode section thereot to provide a control potential across load resistor 43 for the input circuit 01! tuning-indicator tube 36. For intermediate-irequency signals oi any usable intensity, a relatively constant negative bias is thus applied to the control electrode 01' indicator tube 38 reducing the shadow angle oi the tube to indicate that the receiver is correctly tuned and reducing the anode conductance of tube 38 to a minimum. Under this condition, the voltage drop across resistor 30, due to the output current 01 tube 36, is small and a normal operating bias is provided for the grid of duplex tube II. will be seen that, due to the delay bias developed across resistor 39, only the peaks the voltage waves supplied by the selective circuit 4|, 42 are effective "to develop a voltage across resistor 43, thus causing the silencing means to be very sensitive to receiver mistuning. It will be understood that resistor 33 can be replaced by a separate source of bias potential without essentially altering the operation of ,the silencing means. The voltage developed across resistor 38 serves as a source of automatic ampification control potential and serves to maintain the intermediate-frequency signal input to the detector and to the limiter-amplifier 31 within a relatively narrow range for a wide variation 0! received signal intensities, while the limiter-ampli fier 31, being eflective to limitto a substantially constant value the maximum amplitude of signals translated thereby, is eflective to derive an intermediate-frequency signal which is substantially free from residual variations in amplitude for rectification by the diode section of tube 31. The rectifier comprising the diode section of tube 31 being coupled to the limiter section of tube 31 by the tuned circuit 4|, 42 sharplyselective to the carrier-frequency signal translated by the limiter-amplifier 31, its load circuit 43, 44 is effective to derive directly from the rectiiier a unidirectional control voltage uitable for use as a silencing bias voltage.

It will be seen that the network just described provides a silencing potential for the receiver, there being substantially no reduction in the sensitivity of the receiver to signal carriers during the operation thereof. Furthermore, it will be seen that the circuit is very sensitive to mistuning. because of the operation oi. limiter-amplifier 31 and since it is responsive only to the for carrier-frequency currents by condenser 84,

and are applied through a coupling condenser 55 to the control electrode of the pentode section of tube 62 utilized as an audio-frequency amplifier. The audio-frequency output of the pentode section of tube 62 is applied through condenser 66 to the control electrode of audiofrequency amplifier 51, the output circuit of audio'irequency amplifier 61 being coupled to loud-speaker ll through a transformer 68, 39.

Furthermore, it-

Automatic amplification control potentials for the receiver are developed by means 01 a separate A. V. C. rectifier circuit comprising a cathode 60, diode-anode I0, and a shunt load circuit including resistors ll, I2, 13. Automatic ampliflcation control potentials derived Irom load circuit'll, 12, I3 are applied over'a circuit comprising resistor 14 room or more of the tubes of amplifier It, oscillator-modulator ll, and intermediate-frequency amplifier l4. A bias potential is provided for the control electrode of the pentode section oi tube 32 through a circuit comprising resistors 15 and I3, resistor 13 being connected by way of resistors I2 and 18 to a suitable source or grid-bias potential indicated as B in the drawing. Resistor 'Il connected to source -B provide a bias potential for audio-irequency amplifier 61.

The operation of the portion of the receiver of Fig. 2 described above, which is conventional, will be apparent from the description which has been given with reference to the operation 01 the receiver of Fig. 1

Coming now to the parts of the circuit of Fig. 2 comprising the present-invention, the tuning eye tube 38 is connected in such manner as to amplify the unidirectional voltage across the load resistors of the automatic volume control source of bias potential, the input circuit oi the indicator tube 36 being connected to resistor 14 through an audio-frequency filter comprising a series resistor I8 and a shunt condenser 19. The output circuit of indicator tube 36 is energized from the source +B through a load resistor 30 provided with an adjustable tap which is connected to the creen grid of the pentode section of tube 62 by way of a voltage divider comprising resistors BI and 32. Resistor 32. connected between the screen grid of the pentode section of tube 62 and the negative terminal of the direct current supply -B, serves to stabilize the operation of the pentode secton of tube 62 and to permit a more complete silencing action. An intermediate-frequency by-pas condenser 83 is coupled between the anode of the pentode section of tube 82 and ground, while a load resistor 84 is connected between its anode and the source of direct current supply +15.

In considering the operation of the portion of the circuit of Fig. 2 comprising the present invention, it will first be assumed that no signal of an appreciable amplitude are being received Under these conditions, as in the case of the circuit of Fig. 1, the control grid of the tuning indicator 36 is substantially at ground potential and the resistance of the output circuit of the indicator tube 36 is low, giving. a wide angle shadow on its target 41 to show that the receiver 1 is not tuned to a sending station. Under the conditions assumed, the anode conductance of tube 36 is high, resulting in an appreciable voltage drop across resistor 83. The voltage drop across the portion of resistor 30 between its tap and the source of direct current supply eflectively reduce the voltage which is normally supplied to the screen grid of the pentode section of tube 62 which reduction efiectively cuts off the tube and silences the receiver. When the receiveris tuned to a signal of any usable strength, the bias voltage developed in the automatic volume control system and applied to the control grid of tuningindicator tube 36 reduces its anode conductance to a very low value. Under these conditions there is no appreciable voltage drop across resistor due to the anode conductance of tube 36 and the screen potential of tube 62 is at its normal value and the received signals are reproduced by the loud-speaker of the receiver in a normal fashion.

It will be understood that the present invention can-be utilized without the tuningindicator feature illustrated in each of the figures, a vacuum tube amplifier of conventional type being utilized in place of tuning-indicator tube 86.

It will be understood that the current or voltage developed in the output circuit of tube 36, or preferably of a conventional amplifier tube used in place of tuning-indicator tube 36, as mentioned in the preceding paragraph, in either of the specific embodiments shown, can be utilized to operate any suitable relay in the signaltranslating channel to silence the receiver. The use of an electromagnetic relay in the silencing circuit has the advantages that its operation is instantaneous during receiver tuning and, furthermore, that its characteristics can be so adjusted that the relay will not operate if the receiver is quickly tuned between two stations remote on the dial, the receiver being silent for all intermediate stations.

As illustrative of a specific embodiment of the invention, the following circuit constants are given for the embodiment of the invention shown in Fig. 2:

Tube 62 Type 638 Tube 6'7 Type 6K6G Tube 36 Type 6N5 Resistor 63 0.5 megohm Resistor 71 1 megohm Resistor 75 l megohm Resistor 77 0.5 megohm Resistor 80 0.5 megohm Resistor 81 2 megohms Resistor 82 2 megohms Resistor 84 0.5 megohm Source of direct current supply voltage 140 volts (+B to ground) Source of direct current supply voltage 12 volts ,(ground to -B) While there have been described what are at present considered to be the preferred embodiments of the invention, it will be understood that variouschanges and modifications may be made therein without departing from the invention, and it is contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. 7

What is claimed is:

l. A modulated-carrier signal receiver including a cathode-ray tuning indicator comprising a cathode, an anode, a control electrode and a target, an automatic amplification control system for said receiver for maintaining the signal amplitude at a given point of said receiver within relatively narrow limits, means comprising a limiter and rectifier including a sharply selective circuit coupled to said point for deriving therefrom a potential substantially free from residual variations in amplitude and applying it to said control electrode, a load circuit for said indicator, and means for deriving a voltage from said load circuit to silence said receiver.

2. A modulated-carrier signal receiver of the superheterodyne type including an automatic am plification control system for maintaining the signal amplitude at a given point in the intermedicases ate-frequency channel of said receiver within relatively narrow limits, means comprising a limiter-amplifier coupled to said point for deriving a signal substantially free from residual variations in amplitude from the intermediate-frequency channel of said receiver, said limiter-amplifier including a sharply selective circuit tuned to the intermediate frequency and following the point at which limiting occurs, and means comprising a rectifier coupled to said limiter-amplifier for deriving a potential to silence said receiver.

3. A modulated-carrier signal receiver of the superheterodyne type including an automatic amplification control system for maintaining the signal amplitude at a given point in the intermediate-frequency channel of said receiver within relatively narrow limits, means comprising a limiter-amplifier coupled to said point for deriving a signal from the intermediate-frequency channel of said receiver substantially free from residual variations in amplitude, said limiteramplifier including a sharply selective circuit tuned to the frequency of said intermediate-frequency channel and following the point at which limiting occurs, and means comprising a rectifier responsive only to the peaks of said derived signal for developing a control voltage to silence said receiver.

4. A modulated-carrier signal receiver of the superheterodyne type including an automatic amplification control system for maintaining the signal amplitude at a given point in the intermediate-frequency channel of said receiver with in relatively narrow limits, means comprising a limiter-amplifier coupled to said point for deriving a signal from the intermediate-frequency channel of said receiver substantially free from residual variations in amplitude, said limiter-amplifier including a sharply selective circuit tuned to the frequency of said intermediate-frequency channel and following the point at which limiting occurs, means comprising a rectifier responsive only to the peaks of said derived signal for developing a control voltage, and a direct current amplifier tube comprising a cathode, an anode and a control electrode, means for applying said control voltage to said control electrode, and means responsive to the anode current of said direct current amplifier tube for silencing said receiver when said control voltage is below a predetermined value.

5. In a carrier-signal receiver, a control network comprising, means for receiving a carrierfrequency signal, an amplitude limiter for limiting to a substantially constant value the maximum amplitude of signals translated thereby, a rectifier, a circuit sharply-selective to said carrier-frequency signal and coupling said limiter to said rectifier, means for applying said carrierfrequency signal to said limiter and rectifier, means for deriving directly from said rectifier a unidirectional control voltage for said receiver which is substantially free from residual variations in amplitude, and means for utilizing said control voltage to control an operating characteristic of said receiver.

6. In a carrier-signal receiver including an automatie. amplification control system for maintaining the signal amplitude at a given point within relatively narrow limits, a control network comprising, means for deriving from said given point a carrier-frequency signal of a predetermined frequency, an amplitude limiter for limiting to a substantially constant value the maximum amplitude of signals translated thereaasaa by, a rectifier, a circuit sharply-selective to said predetermined frequency and coupling said limiter to said rectifier, means for applying said control signal to said limiter and rectifier, means .for deriving directly from said rectifier a unidirectional control voltage for said receiver which is substantially free from residual variations in amplitude, and means for utilizing said control voltage to control an operating characteristic of said receiver.

7. In a carrier-signal receiver, a control network comprising, means Ior receiving a carrierfrequency signal, an amplitude limiter for limiting to a substantially constant value the maximum amplitude of signals translated thereby, a rectifier, a circuit sharply-selective to said carrier-frequency signal and coupling said limiter to said rectifier, means ior applying said carrierfrequency signal to said limiter and rectifier, means for limiting the operation 0! said rectifier to derive directly from said rectifier a unidirec tional control voltage for said receiver responsive only to the peaks oi. the limited and selected signal which is substantially free from residual variations in amplitude, and means for utilizing said control voltage to control an operating characteristic oi said receiver.

8. In a carrier-signal receiver, a control network comprising, means for receiving a carrierirequency signal, an amplitude limiter for limiting to a substantially constant value the maximum amplitude of signals translated thereby, a rectifier, a circuit sharply-selective to said carrier frequency and coupling said limiter to said rectifier, means ior applying said control signal to said limiter and rectifier, means including an amplitude delay bias for said rectifier to limit the eiiective operation thereof only to the peaks of said carrier-frequency signal for deriving directly from said rectifier a unidirectional control voltage for said receiver responsive only to the peaks of said carrier-frequency signal and which is substantially free from residual variations in amplitude, and means for utilizing said control voltage to control an operating characteristic of said receiver.

NELSON P. CASE. 

